1. Field of the Invention
The present invention relates to an attractant for use in bait compositions and/or traps for social insects, particularly ants and more particularly fire ants. It also relates to the use of these compositions to control social insects.
2. Description of the Related Art
Attractants for insect control are used to lure insects to a toxicant and/or trap. They also can be used to identify the presence, distribution and population of an insect. Most commercially available baits for pest social insect control use a vegetable oil, such as soybean oil, or a sugar which act as phagostimulants in the baits. The oil is also the solvent for the active ingredient which is usually a toxicant. The solution is then absorbed onto an inert carrier, typically pre-gel defatted corn grits. The formulation can then be spread effectively to allow foraging insects to harvest the grits, taking them and the active ingredient into the nest. In the nest the liquid is sucked out of the grits and distributed to other colony members including the queen. The toxic baits take advantage of social insect foraging and food distribution systems to direct the toxicant to the entire colony. Thus, smaller quantities of insecticide are used then would be required for the inundation of colonies with, for example, insecticide emulsions (drenches). Thus, an effective attractant will facilitate the discovery and distribution of an active ingredient to an entire colony of social pest insects.
Control of social insects such as ants, yellow jacket wasps, other pest wasps and termites has long been a problem. Various species of ants pose significant problems for man from both an agricultural and a health care point of view. Leaf-cutting ant species can defoliate a citrus tree overnight. Argentine ants endanger crops by domesticating and protecting other pest insects such as aphids and scale. Fire ants are particularly destructive by stinging humans and livestock, feeding on germinating seeds and crop seedlings thereby reducing yields, damaging electrical equipment and damaging farm machinery which strike the ants' mounds.
Requirements for an effective pesticide formulation for the control of pest social insect species, such as ants, are very stringent because the reproductive forms (queens) of social insects are buffered from the effects of insecticides by a large worker force and their often closed nest structure. Thus, control of social insect pests is inherently different from control of non-social insects. For example, a mature fire ant colony may contain 250,000 sterile workers and a single queen. Only 10 percent of the workers are on the surface foraging for food. Insecticide treatment with a fast acting insecticide will not affect the 90% of the workers in the nest or the queen and the total effect is negligible. In fact, 95% of the workers can be killed, but if the queen is unaffected, the colony will come back. Thus, an effective social insect toxicant must exhibit delayed toxicity, not repel the insects and be effective over a range of concentrations. Repellency can reduce or negate the effectiveness of a toxicant because the insects will avoid a treated bait. A bait must be of a form that is transferable either by carrying it back to the nest or by trophallaxis and the toxicity must be delayed because foraging worker insects constitute only a small percentage of the total colony and must survive long enough to pass the toxicant onto the main colony population, especially the queen(s).
Identification of attractants is important in the development of integrated pest control programs. Most commercially available baits are formulated with either a vegetable oil or a sugar. U.S. Pat. No. 5,104,658 to Hagarty discloses an insecticidal bait composition which is effective against ants, centipedes, earwigs, firebrats, German cockroaches, harvestmen, millipedes, sowbugs, spiders and ticks. This composition includes the sugar maltose, pulverized cereal, animal or vegetable oils as the phagostimulant.
U.S. Pat. No. 4,985,413 to Kohama et al discloses a bait composition that is effective against a wide range of harmful insects such as cockroaches, pillbug, beetles, and ants including Monomorium pharaonis, Monomorium niponense, Lasius fuliginosus and Formica japonica. The composition includes crystalline cellulose, vegetable oils such as soybean oil, rapeseed oil, sesame oil, wheat germ oil, etc.; crop product powders such as potato starch, sweet potato starch, corn starch, wheat flour, rice powder, corn powder, etc.; a saccharide such as sugar, glucose, D-fructose, lactose, black sugar, brown sugar, soft brown sugar, etc.; and an insecticide.
There are many reports on volatiles that contain attractive chemicals for insects. Tsuboi et al (J. Org. Chem., Volume 47, 4478-4482, 1982) report that certain insect pheromones have conjugated E,Z-diene systems. They also disclose that(2E,4Z)-Dienoic esters are important compounds having utility as aroma agents for food, drinks and tobacco. The reference is directed to synthetic methods for 2E,4Z-Dienoic esters and is silent on the use of these compounds as attractants in baits for the control of social pest insects. Buttery et al report that (E,Z)-2,4-heptadienal is a component in the volatile oil extracted from leaf-cutter bee cells obtained from a number of different natural nesting sites. However, the reference is silent as to any activity of this component of the extracted volatile oil. Wassgren et al (J. Insect Physiol., Volume 38 (11), 885-893, 1992) report the presence of (E,E)-2,4-heptadienal and (E,E)-2,4-decadienal in whole body extracts of female pine sawflies but the reference states that the function of these two compounds is unknown and notes that these two components have a structural relationship to (E,Z)-2,4-decadenoate which is a pheromone component of the spruce engraver beetle. Pierce et al (Journal of Chemical Ecology, Volume 16 (2), 465-475, 1990) disclose that two olefinic oat volatiles, 2(E),4(E)-heptadienal and 3(E),5(E)-octadien-2-ol were attractive at 0.1-10 .mu.g for the beetle O. surinamensis (sawtoothed grain beetle) and O. mercator (merchant grain beetle). However, the reference fails to specifically mention the use of these compounds in baits.
There remains a need in the art for highly effective attractant formulations for the control of social pest insects. The present invention provides an attractant for use in baits and/or traps for the control of social pest insects that is different from related art attractants.